The theory and use of electromagnetic surface waves has been well documented. The term “surface waves” covers a broad range of electromagnetic phenomena concerning the propagation of radio waves across a surface. Specifically, a surface wave is one which interacts with a surface in order that the wave propagates across that surface. In the field of radio transmission, the interaction between radio waves and the poorly conductive surface of the earth is commonly referred to as surface wave propagation.
In the field of radio transmission, the use of surface waves to transmit radio signals over long distances is well known. One of the characteristics of a surface wave, which makes it suitable for radio transmission, is the ability of the wave to “cling” to the surface, and therefore follow the curvature of the earth. This is in contrast to typical electromagnetic propagation, which generally propagates in a straight line.
Within the field of surface waves, there are a number of different electromagnetic phenomena which result in different types of surface waves. One phenomenon by which radio waves propagate across the surface of the earth is known as the Norton surface wave. The Norton surface wave is the component of the electromagnetic field closest to the homogeneous conducting ground when an electromagnetic wave is launched over it. This may be done, for example, by a dipole. The Norton surface wave requires a space wave component above the surface to exist. As noted above, there are a number of technologies that claim to utilise Norton surface waves for “over-the-horizon” communications and radar.